NEWTOWN, Conn. – The gunman in the Connecticut shooting rampage was carrying an arsenal of hundreds of rounds of especially deadly ammunition — enough to kill just about every student in the school if given enough time, authorities said Sunday, raising the chilling possibility that the bloodbath could have been even worse.

Hours later, President Barack Obama told mourners at a vigil that the nation is failing to keep its children safe. He pledged to seek change in memory of the 26 staffers and schoolchildren who were killed in the second-deadliest school shooting in U.S. history.

"What choice do we have?" Obama said. "Are we really prepared to say that we're powerless in the face of such carnage, that the politics are too hard?"